Blends of two or more polymers have often been made, for example in attempts to combine desirable properties of the individual polymers into the blend, to seek unique properties in the blend, or to produce less costly polymer products by including less expensive polymers in the blend. Many attempts have been made to blend polyamide resins, such as nylon-6 and nylon-6,6, and polyolefin materials. Polyamide resins have excellent chemical and abrasion resistance, good oxygen barrier properties, good electrical properties, and superior mechanical strength, but are very moisture sensitive and are difficult to process due to their high melting temperature. Polypropylene is a low cost, low density semi-crystalline polymer with excellent moisture resistance that is capable of being recycled and is easy to process.
However, it is difficult to obtain a good dispersion of a polar polyamide resin and a nonpolar polyolefin resin. It is known that the addition of a graft or block copolymer of similar chemical structure to the blend components can improve the quality of the dispersion. These copolymer additives, generally referred to as compatibilizers, are often added to the blend as a third component.
Maleic anhydride-grafted polypropylene has been used as a compatiliblizer for polypropylene/nylon blends. For example, a graft copolymer that is the reaction product of a styrene/maleic anhydride copolymer and a functionalized thermoplastic polymer, such as polypropylene grafted with carboxylic acid-containing monomers, is added to a polyamide and, optionally, polypropylene, as disclosed in U.S. Pat. No. 5,244,971. The styrene copolymer can be based on styrene and/or alpha-methylstyrene and maleic anhydride and optionally an acrylate or methacrylate and/or acrylonitrile. U.S. Pat. No. 5,317,059 discloses a polymer composition comprising (1) at least one olefin polymer, (2) at least one polyamide, (3) a compatibilizing agent that is at least one terpolymer of an alpha-olefin, an acrylic ester, and an unsaturated dicarboxylic acid reagent or a glycidyl acrylate, and optionally (4) an auxilliary compatibilizing agent. U.S. Pat. No. 5,665,820 discloses the use of an elastomeric polypropylene modified with an unsaturated grafting monomer and/or blends thereof with isotactic polypropylene modified with an unsaturated grafting monomer as a compatibilizer for a blend of a polyamide and a polyolefin. The grafting monomers used include unsaturated mono-or dicarboxylic acids or anhydrides or esters thereof, esters of vinyl alcohol, vinyl aromatic compounds, and mixtures thereof. U.S. Pat. No. 5,234,993 discloses a blend of at least one polyamide and a crystalline polyolefin containing a compatibilizing rubbery polymer such as an ethylene/propylene/diene rubber grafted with at least one of maleic anhydride and glycidyl methacrylate.
However, there is still a need for a material that will produce a homogeneous polyamide/polyolefin blend with improved impact resistance and an improved balance of strength and stiffness.